1. Field of the Invention
The present invention relates to a liquid droplet ejecting apparatus and a liquid droplet ejecting method.
2. Description of Related Art
In the liquid droplet ejecting head in which liquid droplets are ejected from a nozzle such as an inkjet recording head (also called recording head hereinafter) for recording images using small ink droplets, liquid droplets are ejected from the nozzle and land on a recording medium such as recording paper and the like by applying pressure to a pressure chamber.
There are various pressure application methods for applying pressure in the pressure chamber, and as disclosed in Patent Document 1, one example is the type in which ink droplet ejection pressure is obtained by using a piezoelectric element.
In the past, in the case where the ink droplets were ejected from the nozzle by increasing the pressure in the pressure chamber by expanding and then contracting the volume of the pressure chamber, the pulse width of the expansion pulse for expanding and then contracting the volume in the pressure chamber was considered to be capable of ejecting most effectively when equal to 1 AL (Acoustic Length), and so this has been used. (See Unexamined Japanese Patent Application No. 2002-19103 publication). The “AL” is a unit of time and 1 AL corresponds to ½ of the acoustic resonance period of the pressure chamber.
However, according to the findings of the inventors, the negative pressure wave that is generated by the expansion dampens with the passage of time when it propagates through the pressure chamber. As a result, it was determined that when damping of the pressure wave is considered, if the pulse width of the expanding pulse is set shorter than 1 AL to which it is set in the aforementioned prior art, ejection can be more efficient.
As is the case in the prior art, when the pulse width of the expanding pulse is set to 1 AL, at the point where the positive pressure exceeds the maximum (peak) and is decreasing, removing application of the expansion pulse is carried out and ejection efficiency is reduced.